1. Field of the Invention
The present invention relates generally to the field of mechanical blowers used in industrial applications, and more particularly relates to double rotor lobe type blowers commonly known as rotary blowers.
2. Description of the Prior Art
Rotary blowers are widely used in industrial applications. In blower terminology, 15 to 25 pound per square inch gage (psig) is generally considered relatively high pressure compared to the conventional medium pressure of 5 to 15 psig. High-pressure blowers are widely used, for example, for deep tank aeration in modern wastewater treatment plant, dilute and dense phase pneumatic conveying of bulk materials, or vacuum applications.
However, the high pressure in 15-25 psig range is difficult to obtain in a single stage compression, mainly due to the higher discharge temperature resulted from higher compression ratio, and more leakage flow at a higher pressure differential from blower discharge to suction side through the gaps within the blower. The recycled hot leakage flow raises the inlet temperature, hence further increases the discharge temperature which is already very high due to higher compression ratio.
In addition, from a mechanical point of view, the raised discharge temperature reduces the internal clearances determined by thermal expansion differential so that it could potentially cause rotor rubbing and total seizure failure. The higher temperature of discharge air also raises the temperature of bearings, timing gears and oil, shortening their life or eventually causing total failure.
For those and other reasons, the pressure capability of rotary blower is generally limited to 5 to 15 psig range for a conventional design. However, rotary blowers are widely desired because of its unique performance characteristics due to its rotary positive displacement nature which delivers an almost constant flow at varying pressure levels. The ability of varying pressure at constant flow makes rotary blowers ideal tools for pneumatic conveying applications where material clogging can be quickly cleared with the increase of pressure. Moreover, higher pressure blowers allow the use of smaller pipes to transfer the same amount of material, which reduces the overall size, weight and cost of the application system.
Various approaches have been developed to address the higher temperature problems, such as spraying liquid into the gas stream, including a liquid jacket on the casing where the fluid is circulated and cooled, or using a forced oil lubrication that in turn is cooled by an external heat exchanger. However, many industrial applications prohibit the use of liquid in the gas stream because it can contaminate the application process or the material that is being transferred. In addition, the water jacket method and the forced oil lubrication procedure increase the cost and complexity of the system.
Moreover, while these conventional approaches attempted to deal with the problems of higher pressure blowers, they fail to address the main cause the of the problems, i.e., the internal leakage of the blowers.
Additionally, higher pressure applications also increase the likelihood of leakage at the blower discharge flange. This becomes very critical when the gas is harmful to humans. The conventional low pressure flanges typically have sealing surfaces around not only the pipe wall, but also the bolt pattern. As a result, high torque is required to tighten the bolts for sealing the surface.
Presently, there are two groups of designs for protecting the blower in case of excessive conditions. They are both constructed in the form of plugs, but are either thermal or pressure actuated, so that a diaphragm member would rupture or break when the temperature or pressure reaches or exceeds certain pre-determined threshold.
For thermally triggered plugs, the diaphragm is made from a solder material having a predictable melting point that corresponds to the maximum temperature permissible in the discharge gas of the blower. For pressure triggered plugs, the diaphragm is a rupture disk that would mechanically break open when pressure differential exceeds the tensile limit of the material.
However, the thermal or pressure triggered plugs used in these existing methods are all one time use plugs. Once they are activated and spent, the blowers must be disabled from operation for certain period of time before new plugs can be re-installed. In addition, there is no audible alarm to alert the failure.
Accordingly, it is always desirable to provide a new design and construction of high pressure rotary blowers that can achieve high pressure rise and pressure ratio while overcome the problems existed in conventional rotary blowers, so that they can operate more safely, efficiently and reliably.
The present invention is directed to a high pressure rotary blower that utilizes cooling fans on rotor shaft, a high-pressure connecting flange, contact friendly wearable strip seals on rotor surfaces, and an audible warning and relieving mechanism integrated with the casing of the blower.
It is an object of the present invention to provide a new and unique design and construction of a rotary blower that can achieve higher pressure rise and pressure ratio than conventional blowers while not using liquid cooling methods.
It is also an object of the present invention to provide a new and unique design and construction of a rotary blower that utilizes cooling fans on rotor shaft to effectively reduce the high temperature caused by the higher pressure.
It is also an object of the present invention to provide a new and unique design and construction of a rotary blower that has smaller clearance and closely separated and contact friendly interface to increase blower efficiency and reliability.
It is also an object of the present invention to provide a new and unique design and construction of a rotary blower with a raised flange surface that seals higher internal pressure more efficiently while requires less torque to tighten.
It is also an object of the present invention to provide a new and unique design and construction of a rotary blower that is equipped with a reusable pressure activated plug for relieving high pressure gas when the internal pressure of the blower exceeds a predetermined limit.
It is also an object of the present invention to provide a new and unique design and construction of a rotary blower that provides audible warning after the pressure relieving plug has been triggered.
In a preferred embodiment of the present invention, the high pressure rotary blower includes a housing structure with a flow suction port and a flow discharge port and internal flow passage there-between. The housing structure includes an inner enclosed casing and an outer cover with a hollow space there-between and one or more cooling air inlet openings and one or more cooling air outlet openings on the outer cover for passing through cooling air. The present invention high pressure rotary blower also includes two parallel three-lobe rotors rotatably mounted on two parallel rotor shafts respectively inside the inner casing and interconnected through a set of timing gears to rotate in synchronization for propelling flow from the suction port to the discharge port. One or more centrifugal cooling fans are mounted on one of the two rotor shafts at locations adjacent to the inlet and outlet openings of the outer cover for circulating cooling air through the space between the outer cover and the inner casing. The present invention high pressure rotary blower further includes a wearable strip seal device applied on the two three-lobe rotors for preventing internal leakage and accidental mechanical contact. In addition, the present invention rotary blower includes a pressure activated relieving device mounted on the inner casing for relieving internal pressure from the blower when it exceeds a pre-determined threshold and producing an audible alarm, and a high pressure discharge flange for the discharge port of the blower having an end sealing surface with a raised center portion. The present invention high pressure rotary blower is capable of achieving higher pressure rise and higher pressure ratio while reducing high pressure induced high temperature and internal leakage, thereby improving the efficiency and reliability of the blower.
The present invention has many novel and unique features and advantages. It provides a new design and construction of a rotary blower that is capable of achieving higher pressure rise and pressure ratio than conventional blowers, without using the conventional liquid cooling methods. It also provides a rotary type blower that has smaller clearance and closely separated interfaces which are contact friendly, to increase the blower efficiency and reliability. The present invention high pressure rotary blower also effectively reduces the higher pressure induced higher temperature on bearing, gear and oil by utilizing internal cooling fans on the gear shaft. In addition, it seals higher internal pressure more efficiently by using a raised flange surface that also requires less torque to tighten. It further utilizes a pressure activated relieving plug that is reusable and provides an audible warning after the pressure release has been triggered.
These and further novel features and objects of the present invention will become more apparent from the following detailed description, discussion and the appended claims, taken in conjunction with the drawings.